A seat belt warning device for providing an indication of the fastened and unfastened states of a vehicle seat belt is described in Japanese Utility Model Unexamined Publication No. Hei. 4-41443. This device issues a warning when the ignition is in the on-state and the seat belt is in an unfastened state. Additionally, the detection of the fastening of the seat belt is inhibited when the opening and closing of the door is not detected.
However, in this type of seat belt warning device, because the detection of the fastening of the seat belt is based on the opening and closing of the door, as long as the door is not opened and closed, the device does not issue a warning, irrespective of the fastened or unfastened state of the seat belt. Thus, it is difficult to detect with certainty the fastened and unfastened state of the seat belt according to the existence of a person sitting in the vehicle seat. Particularly, in the case of detecting the fastened and unfastened state of a seat belt at the passenger seat, if the door is opened and closed, there is a fear that a warning is issued because of the unfastened state of the seat belt, although a person is not actually seated on the seat.
In light of the foregoing, a need exists for a seat belt warning device that is able to reliably detect the fastened and unfastened state of the seat belt based on whether an individual is seated on the vehicle seat.